Place a feeler gauge between the front of the cylinder and the back of the barrel. Many of these old Colt SAA's are worn and the gap becomes too large and lets a lot more gas out between the gap. Many can be fixed with a new bushing in the cylinder. Also, as someone else stated you need to determine the age of the pistol because those made before 1901 generally only use black powder loads and those early ones after 1901 are generally shot with "cowboy" loads that run under 800 fps. You never, ever want to use some of the more modern "hot" loads in these older guns. Go to the Colt forum for specific advice. Many of the folks there are collectors and experts on the Colts. Out of all the pistols in my collection my 1903 Colt .45 SAA bought originally by my greatgrandfather is my favorite pistol to shoot.